Effects Of Dietary Glycyrrhetinic Acid On Growth Performance,Antioxidant Capacity And Quality Of Blunt Snout Bream(Megalobrama Amblycephala)

This study was conducted to examine the effects of dietary glycyrrhetinic acid(GA)on growth performance,lipid deposition and antioxidantic activities of blunt snout bream(Megalobrama amblycephala).And the effects of dietary supplemental GA on weight gain,body composition,intestinal digestive enzymes activities,blood biochemistry results,enzyme activity of lipid metabolism and antioxidantic activities of blunt snout bream.The experiment included four parts.Experiment 1 Effects of dietary glycyrrhetinic acid on growth performance and body composition of blunt snout breamAn 8-week feeding trial was conducted to investigate the effects of dietary glycyrrhetinic acid on growth performance and body composition of blunt snout bream,Megalobrama amblycephala.The basal diet contained 32.44%crude protein and 7%ether extract.Triple groups of fish(initial average weight 15.63 ± 0.04 g)were fed thrice daily with five isonitrogenous and isoenergetic diets containing 0(control group),0.15,0.30,0.45 and 0.6 g/kg GA,respectively.The results indicated that dietary GA levels had little effects on weight gain(WGR),specific growth rate(SGR),feed conversion ratio(FCR),whole body(P>0.05).Weight gain(WGR)of fish fed 0.30 g/kg GA was slightly higher than other group,however feed conversion ratio(FCR)of fish fed 0.30 g/kg GA was slightly lower than other groups(P>0.05).However,the viscerosomatic index(VSI),hepatosomatic index(HSI),intraperitoneal fat ratio(IFR)of fish fed GA supplemented diets were all significantly lower than those of the control group(P<0.05).HSI of fish fed 0.30 g/kg GA was significantly lower than the control group and 0.60 g/kg GA group(P<0.05).VSI of fish fed 0.15 g/kg GA was slightly lower than other groups(P>0.05).Dressout percentage(DP)of fish fed 0.45-0.60 g/kg GA was slightly lower than that of the control group(P>0.05).Moisture and protein content of whole body of fish fed 0.45 g/kg GA was slightly higher than other groups(P>0.05).Lipid content of whole body of fish fed 0.30 g/kg GA was slightly lower than other groups(P>0.05).Lipid content of carcass compositon of fish fed 0.45 g/kg GA was significantly lower than the control group and 0.60 g/kg GA group(P<0.05).Compared with the control group,moisture,protein content,ash content of carcass compositon of fish fed with GA diets was higher slightly(P>0.05).Experiment 2 Effects of dietary glycyrrhetinic acid on antioxidant,blood biochemistry results and intestinal digestive enzymes activities of blunt snout breamThis study was conducted to evaluate the effects of dietary glycyrrhetinic acid on antioxidant,blood biochemistry results and intestinal digestive enzymes activities of blunt snout bream.The conceptual design was the same to the first experiment.The results indicated that dietary GA levels had significantly effects on protease activity,lipase activity,akp activity of intestinal(P<0.05).Protease activity of fish fed 0.30-0.45 g/kg GA was significantly higher than the control group(P<0.05).GA had no significant effect on amylase activity,y-GT activity,Na+,K+-ATPase activity(P>0.05).Amylase activity of fish fed 0.30 g/kg GA was slightly higher than other groups(P>0.05).However,akp activity of fish fed 0.30 g/kg GA was significantly higher than other groups(P<0.05).Na+,K+-ATPase activity of fish fed 0.45 g/kg GA andy-GT activity of fish fed 0.15 g/kg GA were slightly higher than other groups(P>0.05).The results indicated that liver superoxide dismutase(SOD)and reduced glutathione activities(GSH)of fish fed GA supplemented diets were both significantly higher than that of the control group,whereas the opposite was true for malondialdehyde content(MDA)(P<0.05).SOD of fish fed 0.30 g/kg GA was lower than other groups.GA had no significant effect on catalase activity(P>0.05).Catalase activity(CAT)of fish fed 0.45 g/kg GA was slightly higher than other groups(P>0.05).Dietary GA levels also had significantly effects on glucose levels,insulin levels,cortisol levels of plasma(P<0.05).Plasma glucose levels of fish fed 0.15 g/kg GA was significantly higher than the control group,0.45-0.60 g/kg GA group(P<0.05).Plasma insulin levels of fish fed 0.45 g/kg GA was slightly lower than other groups,but the cortisol levels of plasma of fish fed 0.45 g/kg GA was opposite.Experiment 3 Effects of dietary glycyrrhetinic acid on tissue lipid content and lipid metabolism enzymes activities of blunt snout breamThis study was conducted to evaluate the effects of dietary glycyrrhetinic acid on tissue lipid content and lipid metabolism enzymes activities of blunt snout bream.The conceptual design was the same to the first experiment.The results indicated that dietary GA levels had significantly effects on liver fat level,total cholesterol(TC)of plasma(P<0.05).Compared with the control group,liver fat level of fish fed 0.45 g/kg GA was significantly lower than the control group and 0.15 g/kg GA group(P<0.05).GA had no significant effect on muscle fat level(P>0.05).Muscle fat level of fish fed GA supplemented diets were all slightly lower than those of the control group(P>0.05).There were no significant effect on triacylglycerol(TG),nonesterified fatty acid(NEFA),high density lipoprotein cholesterol(HLPC)of fish fed GA supplemented diets(P>0.05).TG of fish fed 0.30 g/kg GA was slightly lower than other groups,but the HLPC of fish fed 0.45 g/kg GA was opposite.Serum cholesterol concentration of fish fed 0.30-0.60 g/kg GA was significantly lower than that of the control group(P<0.05).Lipoprotein lipase(LPL),hepatic lipase(HL)and total lipase activities of fish fed GA supplemented diets were all significantly lower than those of the control group(P<0.05).Lipase activity increased significantly in the groups fed on diets adding 0.30-0.60 g/kg GA(P<0.05).LPL,HL,total lipase activities of fish fed 0.45 g/kg GA was lower than other groups.HL,total lipase activitie of fish fed 0.45 g/kg GA was significantly lower than the control group and 0.15 g/kg GA group(P<0.05).Experiment 4 Effects of dietary glycyrrhetinic acid on off flavor removal capacity of blunt snout breamThis feeding trial was conducted to investigate the effects of dietary glycyrrhetinic acid on off flavor removal capacity of blunt snout bream.Triplicate groups of fish(initial average weight 48.45 ± 0.76 g)were fed thrice daily with two isonitrogenous and isoenergetic diets containing 0(control group),0.30 g/kg GA,respectively.There were two sets of independent culture systems.One was natural water,another has 1μg/L 2-methylisoborneol(MIB).The results indicated that in 4,6-week,GA,MIB has no significant effect on growth performance(P>0.05).In 6-week,weight gain(WGR),specific growth rate(SGR)of fish fed 0.30 g/kg GA was slightly higher than other groups(P>0.05).In 4-week,GA,MIB has no significant effect on hepatosomatic index(HSI),intraperitoneal fat ratio(IFR),condition factor(CF)(P>0.05).However,MIB levels had significantly effects on viscerosomatic index(VSI),dressout percentage(DP)(P<0.05).In 6-week,GA,MIB has no significant effect on VSI,IFR(P>0.05).MIB levels had significantly effects on HIS(P<0.05).CF and DP of fish fed 0.30 g/kg GA was higher than other groups(P<0.05).In 4,6-week,GA,MIB had significantly effects on Off flavour in muscle of blunt snout bream(P<0.05).The results indicated that 0.30 g/kg GA could reduce the level of Off flavour in muscle(P<0.05).In addition,GA also could improve the taste in muscle of blunt snout bream.In conclusion,dietary inclusion of 0.30-0.45 g/kg GA could reduce the lipid deposition.The mechanism may be that GA could strengthen lipid degradation and enhance lipid metabolism enzymes activities.Moreover,the GA supplemented diets can promote antioxidant capacity in blunt snout bream.